In the oil and gas industry, it is desirable to obtain data from a wellbore. Several real time data systems have been proposed. One involves the use of a physical cable such as an electrical conductor or a fiber optic cable that is secured to the tubular body. The cable may be secured to either the inner or the outer diameter of the pipe. The cable provides a hard wire connection that allows for real-time transmission of data and the immediate evaluation of subsurface conditions. Further, these cables allow for high data transmission rates and the delivery of electrical power directly to downhole sensors.
It has been proposed to place a physical cable along the outside of a casing string during well completion. However, this can be difficult as the placement of wires along a pipe string requires that thousands of feet of cable be carefully unspooled and fed during pipe connection and run-in. Further, the use of hard wires in a well completion requires the installation of a specially-designed well head that includes through-openings for the wires.
Various wireless technologies have been proposed or developed for downhole communications. Such technologies are referred to in the industry as telemetry. Several examples exist where the installation of wires may be either technically difficult or economically impractical. The use of radio transmission may also be impractical or unavailable in cases where radio-activated blasting is occurring, or where the attenuation of radio waves near the tubular body is significant.
The use of acoustic telemetry has also been suggested. Acoustic telemetry employs an acoustic signal generated at or near the bottomhole assembly or bottom of a pipe string. The signal is transmitted through the wellbore pipe, meaning that the pipe becomes the carrier medium for sound waves. Transmitted sound waves are detected by a receiver and converted to electrical signals for analysis.
In the downhole application of acoustic telemetry wireless networks, communications reliability and range are two highly desirable performance issues. While the use of a single piezoelectric transducer with an associated transceiver offers fabrication advantages, design compromises can impact performance. For example, one major drawback of the single transducer/transceiver design is that both transmitter and receiver performance may be compromised in order to accommodate the single transducer design.
Accordingly, a need exists for alternative electro-acoustic communications node designs, for use in wellbore acoustic telemetry systems, which offer improved communications performance.